original state despite attack of the environment. The ability of the 

 structure to withstand environmental attack is called durability. 



Concrete is an extremely durable material and ranks high among all 

 known structural materials for its resistance to the attack of natural 

 environments. Freeze-thaw and saltwater immersion tests have demonstrated 

 the inherent resistance of concrete. It is generally accepted that properly 

 designed prestressed concrete piles are among the most durable piling for 

 marine structures, even in a tropical salt-spray environment. 



Maintenance of durability is achieved only by proper design and con- 

 struction. The consequences of disintegration and corrosion are poten- 

 tially catastrophic. Corrosion and disintegration are not random or spot 

 occurrences. Rather, when disintegration and disruption do take place, it 

 is usually due to some fundamental error or neglect; the damage often 

 extends to the entire structure. Thus, except for some localized spot of 

 impact or accident, if disintegration is found, a thorough investigation 

 should be made of the entire structure. 



b. Impacts on Durability . 



(1) Disruption. Durability is affected by disruption of concrete 

 structure, environmental attacks, and use of aggregates. Disruption may 

 take several forms: 



(a) Disintegration of the concrete; 



(b) chemical replacement in the concrete with a consequent 

 loss of strength; 



(c) corrosion of reinforcing bars and ties or prestressing 

 tendons, causing loss of strength, fracture, or lower resistance to 

 fatigue; 



(d) corrosion of the inserts, embedded fittings, and connec- 

 tions ; and 



(e) corrosion of anchorages. 



In combination these forms may interact to intensify disruption. For 

 example, corrosion of reinforcing bars produces products that swell and 

 cause disintegration of the concrete cover. 



(2) Environmental Attacks . Exposure to environmental elements may 

 result in attacks that could severely impair the serviceability of a 

 concrete structure if it were not made sufficiently durable. Among the 

 more common environmental attacks are the following: 



(a) Those causing or accelerating disintegration of or 

 change in the concrete: 



(1) Reactive aggregates; 



(2) unsound aggregates; 



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